The present invention relates to a mobile communication device for use in a system connected by a TDMA scheme between a base station and a plurality of mobile stations, such as a digital cordless telephone system and a celluler communication system.
In recent years, various mobile communication systems have been developed with an advance in the communications technique and a growing need for communications. As one of them there is a digital cordless telephone system called a PCS (personal communication system).
This type of system comprises, as shown in FIG. 8 for instance, a plurality of base stations CS1, CS2, CS3, . . . connected via wire telephone lines to the public switched telephone network NW and a plurality of mobile stations PS1, PS2, . . . connected via radio channels to these basic stations CS1, CS2, CS3, . . . The respective mobile stations PS1, PS2, . . . make their mutual communication via the corresponding base stations or relative to the corresponding subscriber terminal connected to the public switched telephone network NW.
Here, a 4 channel TDMA (time division multiple access)--TDD (time division duplex) scheme is adopted as a radio access scheme between the base stations CS1, CS2, CS3, . . . and the mobile stations PS1, PS2, . . .
The radio access scheme has a transmission signal frame, that is, a signal frame transmitted on a plurality of radio carriers f1 to fm, comprised of four time slots FL1 to FL4 for forward link used for communication from the respective mobile station to the corresponding base station and four time slots RL1 to RL4 for reverse link from the base station to the corresponding mobile station, as shown in FIG. 9 for instance. The radio communication is done between the mobile station and the base station by allocating, as information channel to the mobile stations, a pair of each of time slots FL1 to FL4 for forward link and a corresponding one of time slots RL1 to RL4 for reverse link. That is, the four information channels are provided for each radio carrier.
In the mobile communication device adopting this type of radio access scheme, an important task is how long the life of a battery unit has to be extended. In order to realize this task, various types of battery saving schemes have thus far been proposed. Some saving scheme is adopted to suppress any unnecessary power consumption by cutting off a power supply from the battery unit to a radio unit in other than those time slots of the information channel allocated to an individual mobile station for instance. This type of conventional system will be set out below.
FIG. 10 is a view showing an arrangement of a radio unit of a mobile communication device adopting this battery saving scheme. In FIG. 10, an operation voltage of a control unit 50 is supplied through a switch SW6 to a local oscillator 14. Further, the operation voltage of a power source unit is supplied via a switch SW7 to a frequency converter 151 and transmission power amplifier 152 in a transmitting circuit. On the other hand, the operation voltage from the power source unit is supplied via a switch SW8 to a frequency converter 131 and amplifiers 132 and 133 in a receiving circuit.
The respective switches SW6, SW7, and SW8 are ON-OFF controlled by corresponding switch control signals output from the control unit 50.
In such arrangement, at a transmission period, the switch SW6 is first turned ON at a time point a predetermined time T1 earlier than a start time point of a transmitting time slot, while giving consideration to a delay rise of the local oscillator 14. For this reason, an operation voltage is supplied from the power source unit to the local oscillator 14 where an oscillation operation is started. Then a switch SW7 is turned ON at a time point a predetermined time T2 earlier than a start time point of the transmitting time slot. For this reason, an operation voltage is supplied from the power source unit to the frequency converter 151 and transmission power amplifier 152 in the transmitting circuit. By doing so, the frequency converter 151 and transmission power amplifier 152 in the transmitting circuit become operative. In this connection it is to be noted that the time T2 is set in accordance with a time taken for a variation in oscillation frequency occurring in the local oscillator 14 at a start time of the frequency converter 151 to converge.
At the period of transmitting time slot, a modulated signal output form a modulation circuit, not shown, is input to the frequency converter 151. In the frequency converter 151, the modulated signal is mixed with the local oscillation signal generated from the local oscillator 14 and is frequency-converted to a signal for a radio carrier. The transmission radio carrier signal, after being amplified by the transmission power amplifier 152 to a predetermined transmitting power level, is transmitted from an antenna, not shown, to the base station.
When the period of transmission time slot is ended, the switch control signal is output from the control unit 50 and the switches SW6 and SW7 are turned OFF. For this reason, the supply of a power from the power source unit to the local oscillator 14 and transmitting circuit is stopped, so that the transmitting system is set in a battery saving state.
At a receiving time, on the other hand, as shown for example in FIG. 12, the switch SW6 is first turned ON a predetermined time T1 earlier than the start time point of the receiving time slot as in the case of the transmitting time. For this reason, an operation voltage is supplied from the power source unit to the local oscillator 14, so that the local oscillator 14 starts its oscillation operation. Then the switch SW8 is turned ON at a time point a predetermined time T3 earlier than the receiving time slot starting time. For this reason, the operation voltage is supplied from the power source unit to the frequency converter 131 and amplifiers 132, 133, so that the frequency converter 131 and amplifiers 132 and 133 are set in an operative state. The time T3, like the time T2, is set in accordance with a time taken for a variation in the oscillation frequency occurring in the local oscillation circuit 14 at a start time of the frequency converter 131 to converge.
When, in this state, the receiving time slot period is entered and the radio carrier signal directed to the corresponding individual mobile station is received by the antenna, not shown, the radio carrier signal, after being amplified by the high frequency amplifier 132, is input to the frequency converter 131. In the frequency converter 131, the radio carrier signal is mixed with the local oscillation signal generated from the local oscillator 14 and frequency-converted to a reception signal of an intermediate frequency or baseband frequency. The reception signal, being amplified by the amplifier 133, to a demodulation circuit, not shown, where it is demodulated.
When the receiving time slot period is ended, the switches SW6, SW8 are turned OFF by the control of the control unit 50 and hence the supply of electric power to the local oscillator 14 and receiving circuit is cut off, so that the receiving system is set in a battery saving state.
That is, in the arrangement above, the respective circuits of the receiving and transmitting systems receive power supply only during the receiving and transmitting time slots and are made in an operative state. And during the other idle period, these circuits are placed in a not-operated state. For this reason, the dissipation power of the mobile station is reduced in comparison with the case where the power is constantly supplied to the respective circuit of the receiving and transmitting systems. By doing so, it is possible to extend the life of the battery unit.
However, the above-mentioned conventional circuit has the following tasks to be solved. That is, the timing of the power supply to the frequency converter is so set as to be adequately earlier than the start time points of the receiving and transmitting time slots, taking into consideration the time taken for a variation in the oscillation frequency in the local oscillator at a start of the frequency converter to converge as set out above. The start times of the respective amplifiers are normally very shorter than the time at which the frequency variation of the local oscillator converges.
Either in the receiving circuit or in the transmitting circuit, the conventional circuit simultaneously control the power supply to the frequency converter and respective amplifiers. In the respective amplifiers, therefore, from the setting of their operative state by the power supply to the starting of their actual signal amplification operation following the reaching of the receiving time slot or transmitting time slot, there occurs an unnecessary power dissipation over a relatively long period of time. Since the transmission power amplifier 152 consumes more power than the remaining circuits, it adversely affects the life of the battery unit, thus offering a bar to effectively achieve an effective battery saving.